Reversibly protected silanes can be used for diverse purposes in a wide variety of applications. The development of reversible protecting groups greatly enhances the current utility of silanes while making novel new applications possible. For instance, reversibly protected silanes are of particular value in applications where room temperature cure and/or adhesion is of value, such as coatings, high resolution imaging, caulks, adhesives, sealents, gaskets, and silicones. Reversibly protected silanes can also be beneficially used in reticulating agents, and in sizing agents, tires, and release coatings.
The incorporation of reversibly protected silanes into coating resins is of particular value. Reversibly protected silanes can be incorporated into coating resins by polymerizing a monomer containing the reversibly protected silane into the resin or by post-addition into the coating formulation. The reversibly protected silane remains protected under basic conditions, such as in a coating formulation that contains a volatile base, for instance ammonium hydroxide. However, deprotection occurs under mildly acidic conditions. Thus, as a coating formulation containing a volatile base dries the volatile base evaporates and deprotection occurs. This allows for controlled room temperature crosslinking to occur with hydroxy-functionalized polymers. Chemical adhesion to hydroxy-group containing substrates, such as metal, glass, and wood, also occurs. This makes coating resins that contain reversibly protected silanes especially valuable for coating metals, glass, and wood. Since such coating formulations that contain reversibly protected silanes are curable at room temperature they are much easier to apply and cure than conventional systems. Benefits associated with using coating formulations that contain reversibly protected silanes are realized in a wide variety of applications including structural coatings, anti-corrosion coatings, and marine biofouling coatings.
U.S. Pat. No. 7,022,803 relates to the synthesis of a latex which can be used in making self-crosslinking water-reducible coating compositions, such as paints, which offer excellent solvent resistance, reduced drying time and improved adhesion to metal and glass. Coatings which are formulated with the latex of U.S. Pat. No. 7,022,803 are environmentally advantageous because they contain no or extremely low levels of volatile organic compounds and additionally offer excellent flexibility and excellent ultra-violet light resistance. This patent more specifically discloses a water-reducible coating composition which is comprised of (1) water; (2) a resin having repeat units which are derived from (a) about 30 to about 75 weight percent vinyl aromatic monomers, (b) about 20 to about 65 weight percent of alkyl acrylate monomers, (c) about 1 to about 8 weight percent alkyl propenoic acid monomers and (d) about 0.5 to about 5 weight percent reversibly protected silane monomers, based on 100 weight percent monomers; (3) a wetting agent; and (4) a defoamer.
U.S. Pat. No. 7,022,803 further discloses a modified silane compound having a structural formula selected from the group consisting of
wherein n represents an integer from 2 to 4; wherein m represents an integer from 1 to about 20; with the proviso that m can represent the integer 0 for structures of formula (3) wherein Z represents the group C(R)R1; wherein X groups can be the same or different; wherein X represents a chemical moiety; with the proviso that X does not represent a methyl group, an ethyl group, or a phenyl group in cases where the modified silane compound is of structural formula (2) wherein n represents the integer 1 or the integer 2 wherein R* represents a hydrogen atom wherein Y represents an oxygen atom wherein Z represents the moiety C(R)R′; wherein R, R1, and R2 can be the same or different and are selected from the group consisting of hydrogen atoms, alkyl groups containing from 1 to about 12 carbon atoms, aryl groups containing from about 6 to about 18 carbon atoms, alkaryl groups containing from 7 to about 18 carbon atoms, alkoxy groups containing from 1 to about 18 carbon atoms, hydroxy groups, and halide atoms; wherein R* is selected from the group consisting of hydrogen atoms, alkyl groups containing from 1 to about 12 carbon atoms, aryl groups containing from about 6 to about 18 carbon atoms, and alkaryl groups containing from 7 to about 18 carbon atoms; wherein R, R1, R2, and R* can be bonded together in any combination in cases where R, R1, R2, and R* are not hydrogen atoms, halide atoms, or hydroxy groups; wherein Y represents a moiety selected from the group consisting of C(R)R′, oxygen, sulfur, nitrogen, and phosphorus; wherein Z represents a moiety selected from the group consisting of C(R)R1, oxygen, sulfur, nitrogen, and phosphorus; with the proviso that Y and Z can not both represent the moiety C(R)R1; wherein the contiguous cyclic ring in formulas (1) and (3) can contain heteroatoms selected from the group consisting of oxygen, sulfur, nitrogen, phosphorus, and silicon in cases where m represents an integer greater than 1; wherein the contiguous cyclic ring in formulas (1) and (3) can be saturated or unsaturated in cases where m represents an integer greater than 1; wherein said alkyl groups, aryl groups, alkaryl groups, and alkoxy groups can contain halide atoms and heteroatoms selected from the group consisting of oxygen, sulfur, nitrogen, phosphorus, and silicon. Modified silanes of these types and similar monomers are also disclosed in U.S. Pat. Nos. 7,034,171, 7,034,175, 7,053,162, 7,057,060, 7,060,773, 7,067,600, 7,074,866, 7,078,471, 7,078,549, 7,084,226, 7,084,289, and 7,109,281.
The above-listed patents disclose synthesis techniques for making reversibly protected silanes. However, these techniques can result in gel formation, the presence of residual hydrogen chloride, and/or require expensive starting materials. In any case, a simple, low cost synthesis technique for preparing reversibly protected silanes which are free of undesirable reaction by-products on a commercial basis is needed.